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Designing, planning, and prototyping a GCP network →hardMultiple ChoiceObjective-mapped

PCNE Practice Question: Designing, planning, and prototyping a GCP network

This PCNE practice question tests your understanding of designing, planning, and prototyping a gcp network. This is a configuration task: choose the command set that satisfies every stated requirement. Small differences — like 'secret' vs 'password' or 'transport input ssh' vs 'all' — change whether the answer is correct. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.

Exhibit

Refer to the exhibit.

Command output:
$ gcloud compute routers get-nat-gateway-info my-router --region=us-central1
natGatewayInfo:
- natName: example-nat
  vm: instance-1
  publicIp: 203.0.113.2
  privateIp: 10.0.0.2
- natName: example-nat
  vm: instance-2
  publicIp: 203.0.113.3
  privateIp: 10.0.0.3
natName: example-nat
  vm: instance-3
  publicIp: 203.0.113.4
  privateIp: 10.0.0.4

A network engineer runs the gcloud command above for a Cloud NAT configured in us-central1. The VPC has 20 instances without external IPs in us-central1. They notice that only three instances have NAT mappings displayed. What could explain this?

Question 1hardmultiple choice

Read the full NAT/PAT explanation →

Exhibit

Refer to the exhibit.

Command output:
$ gcloud compute routers get-nat-gateway-info my-router --region=us-central1
natGatewayInfo:
- natName: example-nat
  vm: instance-1
  publicIp: 203.0.113.2
  privateIp: 10.0.0.2
- natName: example-nat
  vm: instance-2
  publicIp: 203.0.113.3
  privateIp: 10.0.0.3
natName: example-nat
  vm: instance-3
  publicIp: 203.0.113.4
  privateIp: 10.0.0.4

A
Only instances with active outbound connections are shown.
NAT gateway info displays only active NAT mappings; idle instances have no mapping.
B
The NAT gateway is configured only for a specific subnet.
Why wrong: The NAT gateway is regional and covers all subnets in the region unless limited by subnet scope.
C
Only instances with external IPs are mapped.
Why wrong: Instances with external IPs do not use Cloud NAT.
D
The other instances are using a different NAT gateway.
Why wrong: The command shows only one NAT gateway for the region.

Full breakdown with real-world context →

Answer choices

Why each option matters

Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.

Correct answer & explanation

✓

Only instances with active outbound connections are shown.

The `gcloud compute nat-gateways list-mappings` command only displays NAT mappings for instances that currently have active outbound connections traversing the Cloud NAT gateway. Cloud NAT uses dynamic port address translation (PAT) and only creates a mapping entry when an instance sends traffic that requires source NAT. Instances without active sessions will not appear in the listing, even though they are configured to use the NAT gateway.

Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.

Answer analysis

Option-by-option breakdown

For each option: why learners choose it and why it is or isn't the right answer here.

✓
Only instances with active outbound connections are shown.
Why this is correct
NAT gateway info displays only active NAT mappings; idle instances have no mapping.
Related concept
Read the scenario before looking for a memorised answer.
✗
The NAT gateway is configured only for a specific subnet.
Why it's wrong here
The NAT gateway is regional and covers all subnets in the region unless limited by subnet scope.
✗
Only instances with external IPs are mapped.
Why it's wrong here
Instances with external IPs do not use Cloud NAT.
✗
The other instances are using a different NAT gateway.
Why it's wrong here
The command shows only one NAT gateway for the region.

Common exam traps

Common exam trap: answer the scenario, not the keyword

The trap here is that candidates assume the `list-mappings` command shows all instances configured to use the NAT gateway, rather than understanding it only shows instances with currently active NAT sessions.

Trap categories for this question

Command / output trap
The command shows only one NAT gateway for the region.

Detailed technical explanation

How to think about this question

Cloud NAT implements RFC 3022-style NAPT (Network Address Port Translation), where each outbound flow is assigned a unique source port from a NAT IP address pool. The `list-mappings` command queries the Cloud NAT's internal state table, which is ephemeral and only contains entries for active sessions. NAT mappings time out after a configurable idle timeout (default 600 seconds for TCP, 30 seconds for UDP), so instances with no recent traffic will not appear. This behavior is analogous to `show ip nat translations` on Cisco IOS, which also only displays active translations.

KKey Concepts to Remember

Read the scenario before looking for a memorised answer.
Find the constraint that changes the correct option.
Eliminate answers that are true in general but not in this case.

TExam Day Tips

Watch for words such as best, first, most likely and least administrative effort.
Review why wrong options are wrong, not only why the correct option is correct.

Key takeaway

Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.

Real-world example

How this comes up in practice

An e-commerce site experiences heavy traffic on Black Friday and near-zero traffic during off-peak weeks. Rather than provisioning permanent large VMs, the team uses auto-scaling groups that add capacity automatically under load and reduce it overnight. Questions like this test whether you understand elasticity, availability zones, and cloud compute scaling patterns.

What to study next

Got this wrong? Here's your next step.

Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.

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FAQ

Questions learners often ask

What does this PCNE question test?

Designing, planning, and prototyping a GCP network — This question tests Designing, planning, and prototyping a GCP network — Read the scenario before looking for a memorised answer..

What is the correct answer to this question?

The correct answer is: Only instances with active outbound connections are shown. — The `gcloud compute nat-gateways list-mappings` command only displays NAT mappings for instances that currently have active outbound connections traversing the Cloud NAT gateway. Cloud NAT uses dynamic port address translation (PAT) and only creates a mapping entry when an instance sends traffic that requires source NAT. Instances without active sessions will not appear in the listing, even though they are configured to use the NAT gateway.

What should I do if I get this PCNE question wrong?

Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.

What is the key concept behind this question?

Read the scenario before looking for a memorised answer.

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Last reviewed: Jun 25, 2026

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